Experiments will be conducted in vivo to compare secretion of growth hormone, prolactin, LH, TSH, insulin, cortisol and testosterone in response to prostaglandin F2 alpha (PGF2 alpha) or PGE2 in bulls. Pituitary cells will be harvested from heifers and bulls, and cultured in monolayers with and without hypothalamic fragments. PGF2 alpha will be added to the culture medium to determine its effect on release of pituitary hormones. Graded doses of PGF2 alpha will be administered into a carotid artery or into a jugular vein to determine whether release of pituitary hormones in response to PGF2 alpha relfects action on the pituitary/hypothalamus or on the periphery. The major goal of this research is to determine the site of action of PGF2 alpha in causing release of pituitary hormones.